1. Field of the Invention
This invention relates to a method for treating diabetes mellitus in an individual in need thereof by administering to the individual a composition comprising a gastrin/CCK receptor ligand and/or an EGF receptor ligand which effectively promotes differentiation of pancreatic islet precursor cells to mature insulin-secreting cells. The method is exemplified by administration of gastrin and transforming growth factor alpha (TGF-xcex1) either alone or in combination to normal streptozotocin (STZ) induced diabetic and genetically predisposed diabetic Zucker rats.
2. Background
Diabetes is one of the most common endocrine diseases across all age groups and populations. In addition to the clinical morbidity and mortality, the economic cost of diabetes is huge, exceeding $90 billion per year in the US alone, and the prevalence of diabetes is expected to increase more than two-fold by the year 2010.
There are two major forms of diabetes mellitus: insulin-dependent (Type 1) diabetes mellitus (IDDM) which accounts for 5 to 10% of all cases, and non-insulin-dependent (Type 2) diabetes mellitus (NIDDM) which comprises roughly 90% of cases. Type 2 diabetes is associated with increasing age however there is a trend of increasing numbers of young people diagnosed with NIDDM, so-called maturity onset diabetes of the young (MODY). In both Type 1 and Type 2 cases, there is a loss of insulin secretion, either through destruction of the xcex2-cells in the pancreas or defective secretion or production of insulin. In NIDDM, patients typically begin therapy by following a regimen of an optimal diet, weight reduction and exercise. Drug therapy is initiated when these measures no longer provide adequate metabolic control. Initial drug therapy includes sulfonylureas that stimulate xcex2-cell insulin secretion, but also can include biguanides, xcex1-glucosidase inhibitors, thiazolidenediones and combination therapy. It is noteworthy however that the progressive nature of the disease mechanisms operating in type 2 diabetes are difficult to control. Over 50% of all drug-treated diabetics demonstrate poor glycemic control within six years, irrespective of the drug administered. Insulin therapy is regarded by many as the last resort in the treatment of Type 2 diabetes, and there is patient resistance to the use of insulin.
Pancreatic islets develop from endodermal stem cells that lie in the fetal ductular pancreatic endothelium, which also contains pluripotent stem cells that develop into the exocrine pancreas. Teitelman and Lee, Developmental Biology, 121:454-466 (1987); Pictet and Rutter, Development of the embryonic encocrine pancreas, in Endocrinology, Handbook of Physiology, ed. R. O. Greep and E. B. Astwood (1972), American Physiological Society: Washington, D.C., p.25-66. Islet development proceeds through discrete developmental stages during fetal gestation which are punctuated by dramatic transitions. The initial period is a protodifferentiated state which is characterized by the commitment of the pluripotent stem cells to the islet cell lineage, as manifested by the expression of insulin and glucagon by the protodifferentiated cells. These protodifferentiated cells comprise a population of committed islet precursor cells which express only low levels of islet specific gene products and lack the cytodifferentiation of mature islet cells. Pictet and Rutter, supra. Around day 16 in mouse gestation, the protodifferentiated pancreas begins a phase of rapid growth and differentiation characterized by cytodifferentiation of islet cells and a several hundred fold increase in islet specific gene expression. Histologically, islet formation (neogenesis) becomes apparent as proliferating islets bud from the pancreatic ducts (nesidioblastosis). Just before birth the rate of islet growth slows, and islet neogenesis and nesidioblastosis becomes much less apparent. Concomitant with this, the islets attain a fully differentiated state with maximal levels of insulin gene expression. Therefore, similar to many organs, the completion of cellular differentiation is associated with reduced regenerative potential; the differentiated adult pancreas does not have either the same regenerative potential or proliferative capacity as the developing pancreas.
Since differentiation of protodifferentiated precursors occurs during late fetal development of the pancreas, the factors regulating islet differentiation are likely to be expressed in the pancreas during this period. One of the genes expressed during islet development encodes the gastrointestinal peptide, gastrin. Although gastrin acts in the adult as a gastric hormone regulating acid secretion, the major site of gastrin expression in the fetus is the pancreatic islets. Brand and Fuller, J. Biol Chem., 263:5341-5347 (1988). Expression of gastrin in the pancreatic islets is transient. It is confined to the period when protodifferentiated islet precursors form differentiated islets. Although the significance of pancreatic gastrin in islet development is unknown, some clinical observations suggest a rule for gastrin in this islet development as follows. For example, hypergastrinemia caused by gastrin-expressing islet cell tumors and atrophic gastritis is associated with nesidioblastosis similar to that seen in differentiating fetal islets. Sacchi, et al., Virchows Archiv B, 48:261-276 (1985); and Heitz et al., Diabetes, 26:632-642 (1977). Further, an abnormal persistence of pancreatic gastrin has been documented in a case of infantile nesidioblastosis. Hollande, et al., Gastroenterology, 71:251-262 (1976). However, in neither observation was a causal relationship established between the nesidioblastosis and gastrin stimulation.
It is therefore of interest to identify agents that stimulate islet cell regeneration which could be of value in the treatment of early IDDM and in the prevention of xcex2-cell deficiency in NIDDM.
Citations of a reference herein shall not be construed as an admission that such reference is prior art to the present invention.
Three growth factors are implicated in the development of the fetal pancreas, gastrin, transforming growth factor xcex1 (TGF-xcex1) and epidermal growth factor (EGF) (Brand and Fuller, J. Biol. Chem. 263:5341-5347). Transgenic mice over expressing TGF-xcex1 or gastrin alone did not demonstrate active islet cell growth, however mice expressing both transgenes displayed significantly increased islet cell mass (Wang et al, (1993) J Clin Invest 92:1349-1356). Bouwens and Pipeleers (1998) Diabetoligia 41:629-633 report that there is a high proportion of budding xcex2-cells in the normal adult human pancreas and 15% of all , xcex2-cells were found as single units. Single xcex2-cell foci are not commonly seen in adult (unstimulated) rat pancreas; Wang et al ((1995) Diabetologia 38:1405 -1411) report a frequency of approximately 1% of total xcex2-cell number.
Insulin independence in a Type 1 diabetic patient after encapsulated islet transplantation is described in Soon-Shiong et al (1994) Lancet 343:950-51. Also see Sasaki et al (Jun. 15, 1998)Transplantation 65(11):1510-1512; Zhou et al (May 1998) Am J Physiol 274(5 Pt 1):C1356-1362; Soon-Shiong et al (June 1990)Postgrad Med 87(8):133-134; Kendall et al (June 1996) Diabetes Metab 22(3):157-163; Sandler et al (June 1997) Transplantation 63(12):1712-1718; Suzuki et al (January 1998) Cell Transplant 7(1):47-52; Soon-Shiong et al (June 1993) Proc Natl Acad Sci USA 90(12):5843-5847; Soon-Shiong et al (November 1992) Transplantation 54(5):769-774; Soon-Shiong et al (October 1992) ASAIO J 38(4):851-854; Benhamou et al (June 1998 ) Diabetes Metab 24(3):215-224; Christiansen et al (December 1994) J Clin Endocrinol Metab 79(6):1561-1569; Fraga et al (April 1998) Transplantation 65(8):1060-1066; Korsgren et al (1993) Ups J Med Sci 98(1):39-52; Newgard et al (July 1997) Diabetologiz 40 Suppl 2:S42-S47.
The invention provides methods for treating diabetes mellitus in a patient in need thereof by administering a composition providing a gastrin/CCK receptor ligand, an EGF receptor ligand, or a combination of both in an amount sufficient to effect differentiation of the patient""s pancreatic islet precursor cells to mature insulin-secreting cells. The composition can be administered systemically or expressed in situ by host cells containing a nucleic acid construct in an expression vector wherein the nucleic acid construct comprises a coding sequence for a gastrin CCK receptor ligand or a coding sequence for an EGF receptor ligand, together with transcriptional and translational regulatory regions functional in pancreatic islet precursor cells. Also provided are methods and compositions for treating diabetes in a patient in need thereof by implanting into a diabetic patient pancreatic islet cells that have been grown in culture by exposure to a sufficient amount of a gastrin/CCK receptor ligand and/or an EGF receptor ligand to increase the number of pancreatic beta cells in the islets from pancreatic islet precursor cells; optionally the population of pancreatic beta cells or pancreatic islet precursor cells can be grown in culture for a time sufficient to expand the population of xcex2-cells prior to transplantation. The methods and compositions find use in treating patients with diabetes.
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